The quality of a semiconductor material can considerably influence the performance of a solid-state device produced from said material. Solid-state devices can suffer from inferior lifetimes and operating characteristics when the semiconductor material has an undesirable density of crystal defects such as, for example, dislocations.
Such problems have hindered the development of semiconductor materials and devices including gallium nitride (GaN), other Group III-nitrides (e.g., AlN, InN, GaInN) and other mixed nitrides (referred to herein as “III-nitrides”) as well as certain Group III-V compounds; and of certain other compound materials (e.g., IV, II-VI materials) generally. For many of these materials, suitable and commercially useful substrates have limited availability and poor crystal quality. A suitable substrate closely matches the crystal properties of the target material to be grown. If these crystal properties do not closely match, the resulting material may have an unacceptable density of dislocations.
Specifically, in the case of GaN, crystal quality can be improved by pre-treating the growth substrates by, for example, nitridization and other chemical modifications, by growing thin, low temperature buffer layers of other III nitrides (e.g., AlN or GaN), by thermal annealing, and the like. Methods such as epitaxial lateral overgrowth (ELO) and its variants (PENDEO, FIELO, etc.) have proven successful in reducing dislocation density. However, these methods often utilize lithographically produced masking elements that often produce materials with a non-uniform distribution of surface dislocations, which may be undesirable in some applications. Alternative methods of reducing the number of dislocations and producing homogenous surface dislocation densities have utilized in-situ (or ex-situ) deposition methods to impede dislocation progression. Examples of such impeding methods are described in, for example, United States Patent Application Publication No. US2007/0259504, which published Nov. 8, 2007 and is entitled “Dislocation-Specific Lateral Epitaxial Overgrowth To Reduce Dislocation Density Of Nitride Films,” Tanaka et al., Japanese Journal of Applied Physics, 39 L831 2000, and Zang et al., Journal of Applied Physics 101 093502 2007. In some instances, these methods may be employed with the addition of etchants to enhance surface dislocation dimensions.
There remains a need in the art for layers and crystals of semiconductor material (e.g., III-nitrides) of improved quality, and for methods of producing such layers and crystals of improved quality.